I can't comment on the Atmos but I had a Stratos 36. I purchased a medium and it didn't fit quite right. I did use it for several hikes before selling it. I did like the pack features like the integrated rain cover and the pockets on the hip belt. I also like the mesh back on the suspension system. I didn't like the stow and go trekking pole rig. The poles got in the way if I was scrambling. I did like the "look" of the pack and it seemed durable enough.